Thermally stable antifoam agent and methods for use in functional fluids

ABSTRACT

A functional fluid contains conventional additives in addition to an antifoam composition. The antifoam compositions contain perfluoropolyether compounds (PFPE). An exemplary functional fluid is an engine oil and engines containing such new engine oil as per the invention exhibit reduced foaming and improved performance. A method of treating the engines comprises adding to the lubricating composition in the sump a top treat composition comprising an antifoam composition of the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. application Ser. No. ______, attorney docket 8540P-000081, filed Nov. 18, 2002.

FIELD OF THE INVENTION

[0002] The present invention relates to functional fluids such as automatic transmission fluids and engine lubricating oils, and more specifically to the use of antifoam agents in the functional fluids.

BACKGROUND OF THE INVENTION

[0003] Automatic transmission fluids (ATF) are non-compressible lubricant compositions containing a number of conventional additives. As typically used, an ATF serves as a hydraulic fluid, activating and engaging gears in the transmission by a series of valves and other hydraulic circuits, and as a lubricant for the hydraulic pump used to provide hydraulic pressure for operation of the transmission. Engine oils are lubricating fluids containing conventional antiwear, antioxidant, and other additives in a mineral oil or synthetic oil base.

[0004] ATF, engine oils, and other functional fluids generally contain detergent and similar additives that tend to produce foam if air is entrained into the fluid. Additionally, impurities are produced in the fluid over time (for example by oxidation or degradation of the base oil), some of which may contribute to a foaming tendency in the functional fluid. Excess foam in a functional fluid can adversely affect its rheological, hydraulic, lubricating, and cooling performance. Entrained air in a hydraulic system fluid such as an ATF is a problem for the further reason that the air alternately expands in the low pressure inlet side of pump, and quickly contracts or is compressed as the fluid passes through the pump to the high pressure outlet side.

[0005] The resulting implosion of air bubbles on the outlet side causes pressure ripples in the hydraulic pump. The pressure ripples can cause objectionable audible noise, manifested as “pump whine” in some transmissions. New automatic transmissions, such as continuously variable transmissions (CVT), with their compact sumps and high pump pressures, have raised the possibility of consumer reaction to the noise. In response, a number of OEM's have taken steps to reduce the air level in the fluid of their new transmissions by isolating or baffling the internal rotating components to separate them from the fluid, or by introducing aeration additives into the ATF to help the oil release the entrained air more quickly or otherwise reduce the level of entrained air. Additionally, conventional antifoam agents have been employed to help dissipate surface air bubbles.

[0006] Antifoams work in part by being insoluble in the process medium. As such, they function in part by having a preferential tendency to reside on the surface of bubbles. However, in hydraulic pumps, the act of adiabatically compressing entrained air on the outlet side causes the surface of air bubbles to reach high temperatures. In some cases the temperature may reach 500° C. or greater. At such elevated temperatures, the antifoam agent is subject to thermal degradation. Because some conventional antifoam agents, such as polydimethylsilicone, are thermally stable only up to about 200° C., they are subject to thermal breakdown in the modern transmission environment.

[0007] Antifoam agents need to be dispersed, but not necessarily dissolved, in the form of liquid droplets above a minimum size in order to be functional. Thermal degradation of the molecules of the antifoam agent inhibits the ability of the antifoam agent molecules to form droplets of effective size. Thermal degradation of the antifoam agent results in antifoam agent molecules that are undesirably further solubilized (i.e. dissolved) in the fluid, such that they are no longer functional as antifoams; they even become forming agents.

[0008] The insolubility of the antifoam agents leads to some difficulties that must be addressed by the formulator of functional fluids such as ATF and engine oils. Typically, the antifoam agent is denser than the base fluids and tends to fall out during shipping and storage before being added to the transmission. In practice, this limits the amount of antifoam agent that can be incorporated or dispersed into the fluid by the supplier. Alternatively, a formulated fluid may be re-dispersed prior to use, but the extra step creates additional expense in the manufacturing process.

SUMMARY OF THE INVENTION

[0009] Many of the difficulties discussed above are overcome and advantages are provided by the use of a new antifoam composition in functional fluids such as ATF and engine oils. The antifoam compositions contain antifoam agents comprising perfluoropolyether compounds (PFPE). In one aspect, a functional fluid is provided containing the antifoam composition in a lubricating base oil, along with conventional additives such as antiwear agents. In a related aspect the functional fluid is an engine oil. In another related aspect, the functional fluid is transmission fluid (ATF). In another embodiment, respectively, engines and automobile transmissions are provided that contain a lubricating engine oil and automatic transmission fluid containing the new antifoam compositions of the invention. In a further embodiment, methods are provided for reducing foam in an automobile engine during operation, comprising lubricating the engine with an engine oil containing the antifoam compositions of the invention. In another embodiment, methods are provided for reducing unwanted noise in an automobile transmission during operation, comprising lubricating the transmission with an automatic transmission fluid containing the antifoam composition of the invention.

[0010] In another embodiment, a method for top treating an engine oil in an automobile engine is provided. The method comprises adding to the fluid in the engine an aliquot of an antifoam composition of the invention. In a further embodiment, methods are provided for manufacture and maintenance of automobile engines. The methods involve top treating an engine containing an engine oil with an aliquot containing the antifoam composition of the invention. Such top treatment may be carried out, for example, at the engine assembly plant, the automobile assembly plant, or in the aftermarket by an automotive repair shop or the consumer.

[0011] In another embodiment, a method for top treating an automatic transmission fluid in an automobile transmission is provided. The method comprises adding to the fluid in the transmission an aliquot of an antifoam composition of the invention. In a further embodiment, methods are provided for manufacture and maintenance of automobile transmissions. The methods involve top treating a transmission containing an automatic transmission fluid with an aliquot containing the antifoam composition of the invention. Such top treatment may be carried out, for example, at the transmission assembly plant, the automobile assembly plant, or in the aftermarket by an automotive repair shop or the consumer.

[0012] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0014] Functional fluid refers to a liquid composition, typically for use in industry, into which it is desirable or necessary to add an antifoam compound. As conventionally used, the term characterizes the fluid by the function it carries out. Non-limiting examples of functional fluids include transmission fluids, hydraulic fluids, lubricating fluids, engine oils, heat transfer fluids, brake fluids, cooling fluids, and the like. The invention is described below by way of non-limiting example with respect to engine oils and transmission fluids.

[0015] In one aspect, a transmission fluid, preferably an automatic transmission fluid (ATF) is provided comprising a lubricating oil, an antifoam composition, and conventional additives. Preferably the transmission fluid contains an antiwear agent present at a level sufficient to provide antiwear protection for the components of the transmission. According to a further embodiment, a transmission is provided comprising a housing defining a lubricant sump. The lubricant sump contains a lubricating oil composition comprising a transmission fluid as discussed above.

[0016] The use of the transmission fluids of the invention provides advantages in reducing the noise or “pump whine” caused by entrained air in the transmission fluid. Thus in a further embodiment, a method for reducing noise during operation of an automobile transmission is provided. The method comprises lubricating the transmission with an ATF as discussed above.

[0017] In a further embodiment, a method of treating a transmission is provided. The transmission contains a housing defining a lubricant sump, and the lubricant sump contains a lubricating composition. The method of treating comprises adding to the lubricating composition in the sump a top treat composition comprising an antifoam composition of the invention.

[0018] In another embodiment, methods are provided for reducing unwanted noise in an operating transmission. The method comprises top treating the lubricating composition in a lubricant sump with a composition containing an antifoam compound that is thermally stable, as measured by differential thermal analysis to a temperature of higher than 200° C., preferably higher than 400° C., and more preferably higher than 500° C.

[0019] In another aspect, an engine oil is provided containing conventional additives in addition to an antifoam composition. An automobile engine lubricated with the engine oil is also provided. The engine containing the antifoam composition exhibits reduced foaming and improved performance.

[0020] In a further embodiment, a method of treating an engine is provided. The engine contains a housing defining a lubricant sump, and the lubricant sump contains a lubricating composition. The method of treating comprises adding to the lubricating composition in the sump a top treat composition comprising an antifoam composition of the invention.

[0021] In another embodiment, methods are provided for reducing foam in an operating engine. The method comprises top treating the lubricating composition in the engine crankcase with a composition containing an antifoam compound that is thermally stable, as measured by differential thermal analysis, to a temperature of higher than 200° C., preferably higher than 400° C., and more preferably higher than 500° C.

[0022] The composition, transmission, engine, and methods of the invention are based on the use of a new antifoam composition for functional fluids. The antifoam compositions of the invention contain perfluoropolyether compounds (PFPE). The PFPE of the invention function to reduce foam in the transmission or engine fluid during operation. The reduction in foam leads to a diminution of noise caused by entrained air in the hydraulic system and to improved performance.

[0023] Perfluoropolyether compounds are polymers containing a plurality of ether groups in the background chain of the polymer, and wherein some or all of the carbon hydrogen bonds of a standard polyether are replaced by carbon fluorine bonds. In one embodiment, the perfluoropolyether compound comprises a plurality of- (C_(a)F_(2a)O)— repeating units wherein a is from 1 to 10. Non-limiting examples of such repeating units include the following:

—(CF₂—CF(CF₃)—O)—

—(CF₂—CF₂—CF₂—O)—

—(CF₂—CF₂—O)—

[0024] In another embodiment, the PFPE compounds contain repeating units of —(C_(b)F_(2b)O)— and (CF₂O)— wherein b is from 2 to 10.

[0025] Perfluoropolyether compounds of the invention can be synthesized by methods well known in the art. In a non-limiting example, they may be synthesized by polymerizing perfluoroolefins in the presence of an oxidizing agent. Non-limiting examples of perfluoroolefins include tetrafluoroethylene and hexafluoropropylene.

[0026] The perfluoropolyether compounds comprise a backbone having repeating perfluoroether units as described above, and in addition are further characterized by two end groups at either end of the perfluoropolyether chain. As described further below, the end groups of the perfluoropolyether compound may be non-functional, in the case of a halogen atom, a perfluoroalkoxy group, and a perfluoroalkyl group, or may contain a number of different functional groups. Non-limiting examples of functional groups include alkyl amide, silane, phosphate, phosphate esters, carboxyl, organic ester, and hydroxyl. Thus, representative structures of perfluoro polyether compounds are given as:

R¹—(—CFCF₃—CF₂—O—)_(n)—R²  (I)

R¹—(—CF₂—CF₂—CF₂—O—)_(n)—R²  (II)

R¹—(—CF²—CF²O—)_(n)—(—CF₂—O—)_(m)—R²  (III)

R¹—(—CF₂—CFCF₃—O—)_(n)—(—CF₂—O—)_(m)—R²  (IV)

[0027] where R¹ and R² comprise the functional or non-functional end groups noted above. As is conventional, the subscripts n and m refer to the number of respective repeating units in the backbone of the PFPE. The values of the m and n determine the molecular weight of the PFPE.

[0028] Generally, PFPE's of the invention should be relatively insoluble in the lubricating base oil of the functional fluid, and have a viscosity in the range of approximately 1 to 150,000 centistokes. The PFPE's generally have a density greater than the lubricating oil, and as such will settle out of the fluid during rest and sit at the bottom of the sump. It is believed that if the viscosity of the PFPE is greater than about 150,000 centisokes, the PFPE will be difficult to re-disperse into the fluid upon operation, especially on cold winter days. Accordingly, PFPE's of the invention are selected with values of n and m such that the viscosity is in the preferred range. As a practical matter, n should be at least about 3. In one preferred commercial embodiment, the sum of m+n is from about 8 to about 45. In another embodiment, the sum of m+n is from about 40 to about 180. PFPE's of formula I are commercially available where n=44-45, where n=19, and with n=13-14. Commercial embodiments of formula IV are available with m+n from 40-180 and the ratio m/n in the range of 0.5-2.0. In another commercial embodiment, the sum of m+n is from 8-45 and the ratio m/n is from 20-1,000. PFPE's of the invention are commercially available, for example under the Fomblin® line of Ausimont or the Krytox® line of DuPont. Non-limiting commercial examples of PFPE's suitable for use in the invention are given in Table 1. TABLE 1 Supplier Tradename Structure Solvey/Ausimont Fomblin W500

Solvey/Ausimont Fomblin M60

Dupont Krytox GPL 107

Dupont Krytox GPL 104

Dupont Krytox GPL 103

Dupont Krytox GPL 105

Solvey/Ausimont Fomblin Y06

Solvey/Ausimont Fomblin M30

Solvey/Ausimont Fomblin Y25

Solvey/Ausimont Fomblin M15

[0029] In the examples given above, the end groups R¹ and R² are respectively selected from the group consisting of fluorine atom, a perfluoroalkoxy group, and a perfluoroalkyl group. In a preferred embodiment, the perfluoroalkyl group is a trifluoromethane group, —CF₃. Other perfluoroalkyl groups include —C_(n)F_(2n+1), wherein n is from 2 to 10. In another preferred embodiment, the perfluoroalkoxy group is a trifluoromethoxy group, —OCF₃. Other perfluoroalkoxy groups include —OC_(n)F_(2n+1), wherein n is from 2 to 10.

[0030] The PFPE of the invention generally exhibit low pour points that allow them to be used advantageously at low temperatures. The pour point is preferably −20° C. or lower, more preferably −40° C. or lower, and even more preferably below −40° C., more preferably −60° C. or lower. In addition, the PFPE exhibit favorable volatility, expressed as evaporation weight loss according to ASTM 2595. Preferably, the percentage weight loss at a given emperature will be 20% or less, more preferably 10% or less, and even more preferably 1% or less, measured at temperatures of 120° C.-204° C. These and other physical properties of some commercially available PFPE of the Fomblin line are given in Tables 2, 3, and 4. TABLE 2 Fomblin Y Lubricant Grades Typical Properties Y04 Y06 Y25 Y45 YR YR1500 YR1800 Approximate ISO grade 15 22 100 150 320 460 460 Molecular weight (AMU) 1,500 1,800 3,200 4,100 6,250 6,600 7,250 Kinematic viscosity (ASTM D445) 20° C. (cSt) 38 60 250 470 1200 1500 1850 40° C. (cSt) 15 22 80 147 345 420 510 100° C. (cSt) 3.2 3.9 10 16 33 40 47 Viscosity index (ASTM 60 70 108 117 135 135 135 D2270) Pour point (° C.) (ASTM D97) −58 −50 −35 −30 −25 −25 −20 Evaporation weight loss (ASTM 2595) 120° C., 22 hr (%) 14 6 — — — — — 149° C., 22 hr (%) — 20 2 0.7 0.5 0.3 — 204° C., 22 hr (%) — — 15 1.7 1.2 0.9 0.5

[0031] TABLE 3 Fomblin Z Lubricant Grades Typical Properties Z03 Z15 Z25 Z60 Approximate ISO grade 15 100 150 320 Molecular weight (AMU) 4000 8000 9,500 13,000 Kinematic viscosity (ASTM D445)  20° C. (cSt) 30 160 263 600  40° C. (cSt) 18 92 157 355 100° C. (cSt) 5.6 28 49 98 Viscosity index (ASTM 317 334 358 360 D2270) Pour point (° C.) (ASTM −90 −80 −75 −63 D97) Evaporation weight loss (ASTM 2595) 149° C., 22 hr (%) 6.0 0.2 — — 204° C., 22 hr (%) n.a. 1.2 0.4 0.2

[0032] TABLE 4 Fomblin M Lubricant Grades Typical Properties M03 M15 M30 M60 Approximate ISO grade 15 100 150 320 Molecular weight (AMU) 4000 8000 9,800 12,500 Kinematic viscosity (ASTM D445) 20° C. (cSt) 30 150 280 550 40° C. (cSt) 17 85 159 310 100° C. (cSt) 5 22 45 86 Viscosity index (ASTM 253 286 338 343 D2270) Pour point (° C.) (ASTM −85 −75 −65 −60 D97) Evaporation weight loss (ASTM 2595) 149° C., 22 hr (%) 6.5 0.8 — — 204° C., 22 hr (%) — 3.0 0.7 0.4

[0033] PFPE of the invention may also include functionalized PFPE, wherein R¹ and R² in formulas I-IV are other than halogen, perfluoroalkoxy, and perfluoroalkyl. Such functional groups include, without limitation, alkyl amide, silane, phosphate, phosphate esters, carboxyl, carboxyl esters, and hydroxyl. If used, the functionalized PFPE should be limited to an amount that does not adversely affect the antifoam property of the antifoam composition containing them. In a preferred embodiment, non- functional PFPE are used along with functionalized PFPE. With this in mind, functionalized PFPE may be chosen for use as antifoam agents.

[0034] In one embodiment, the end groups R¹ and R² are independently represented by A₁-CF₂O— and —CF₂-A², respectively. The groups A¹ and A² may be the same or different, and may be hydrogen, fluorine, or chlorine. In a preferred embodiment, at least one, and preferably both, of A¹ and A² comprise functional groups including carboxyl, amide, silane, hydroxyl, and phosphate. Non-limiting examples of A¹ and A² include

—CONHR_(H);

-Ak-OH;

-Ak-Si(OR_(H))₃;

—COORH;

—CH₂(OCH₂CH₂)_(p)OH;

—CH₂OCH₂CH(OH)CH₂OH; and

-Ak-OP(O)(OH)₂

[0035] wherein R_(H) is H or an alkyl group with 1 to 10 carbon atoms, Ak is a bond or an alkylene group with 1 to 10 carbon atoms, and p is from 1 to about 20.

[0036] In another embodiment, the PFPE are represented by a formula Cl(CF₂CFCF₃O)_(n)CF₂-B, wherein B is the same as A¹ or A² above.

[0037] Functionalized PFPE are well known in the art and are commercially available. For example, they are available under the Fluorolink® line from Ausimont and under the Krytox line of Dupont. Non-limiting examples of commercially available functionalized PFPE are given in Table 5. TABLE 5 Supplier Tradename Structure Solvey/Ausimont Fluorolink S10

Solvey/Ausimont Fluorolink F10

Solvey/Ausimont Fluorolink D10H

Solvey/Ausimont Fluorolink T10

Dupont Krytox Alcohol TLF- 8976

Dupont Krytox Phosphate KDP-4413

[0038] Silane functionality is illustrated by the —Si(OEt)₃ groups of Fluorolink S10. The PFPE's may be monofunctional, difunctional, trifunctional, or tetrafunctional. For example, Krytox Alcohol TLF-8976 in the Table has a single hydroxyl functional group. Fluorolink DIOH illustrates difunctional hydroxyl PFPE's, while Fluorolink T10 is a non-limiting example of a tetrahydroxy functional PFPE. In further non-limiting examples, phosphate functional PFPE's may be monofunctional or difunctional. These are illustrated by Krytox Phosphate KDP-4413 and Fluorolink F10, respectively, in the table.

[0039] Effective defoaming capability of the PFPE of the invention depends in part on its insolubility in the process medium in which it acts. The antifoam additive is dispersed as a second liquid phase. The second phase has a tendency to segregate itself to reside at liquid air interfaces, including bubbles, due to its limited solubility. Although the insoluble nature of the antifoam compounds leads to its antifoam performance, the insolubility imposes limitations on the maximum concentration that can be blended into a stable dispersion with suitable shelf life for commercial use. The PFPE's of the invention may be blended into functional fluids with high shear blending processes to mix in a limited concentration of antifoam agent. As discussed further below, it is also possible to make supplemental additions, or “top treats” of the PFPE's of the invention directly into the functional fluid. Whenever the PFPE is added, it is preferred to use a PFPE having a viscosity in the range of about 1-150,000 centistokes to allow for blending into the fluid, either at the formulator's facility with high shear blending equipment, or in use such as in the sump of an automatic transmission system or the crankcase of an engine, by way of non-limiting example.

[0040] Treat levels of the PFPE's of the invention should be as low as practical to avoid excessive costs, but should be at levels sufficient to reduce the foam and the cavitation or pump whine noise associated with the foam. Generally, the PFPE should be present in the functional fluid at a level from about 5 ppm (0.0005%) to about 1% by weight. More preferably, the maximum level of PFPE is 0.5%, and more preferably the functional fluid contains up to 0.3% by weight of the PFPE. In a preferred embodiment, PFPE is added to the fluid at a level of 0.0005% to 0.269% by weight. In a continuously variable transmission having a sump volume of 8 liters, for example, 3 mL of a PFPE of the invention may be injected. Treatments for the sump of an engine, which is generally defined by the crankcase and the engine block, may be calculated in a similar way, with sump volumes ranging from 3-5 liters and less for automobile engines to several multiples of that for commercial vehicles. In another embodiment, a treat level of 0.188% by weight is used. It is preferred to inject the PFPE into the functional fluid as a solution in a base oil. For example, a top treat composition may be made up comprising 3 mL of PFPE and 7 mL of a lubricating oil. The top treat composition is then added to the functional fluid, such as an automatic transmission fluid or engine oil, in the sump.

[0041] The treatment level of PFPE in functional fluids will be influenced by the presence of other performance additives in the fluid, especially as the other additives affect the amount of air entrainment in the fluid. Examples of such additives include pour point depressants, viscosity index improvers, antioxidants, corrosion inhibitors, extreme pressure agents, antiwear agents, and other antifoam agents. The blended engine oils and other functional fluids containing the antifoam compositions of the invention preferably exhibit a flash point greater than about 170° C., withstand oxidation, suppress volatilization, and resist breakdown. Further, they should exhibit non-foaming characteristics at high temperatures and pressures and low viscosity at low temperatures.

[0042] The PFPE antifoam compositions may be used in a variety of functional fluids, including engine oils and ATF. By way of illustration but not of limitation, the practice of the invention will be described further below with respect to ATF.

[0043] In addition to the base lubricating oil and the PFPE antifoam compounds, formulated ATF's contain a number of other conventional additives such as:

[0044] boronated or non-boron dispersants;

[0045] anti-oxidation compounds;

[0046] seal swell compositions;

[0047] friction modifiers;

[0048] extreme pressures/antiwear agents;

[0049] viscosity modifiers;

[0050] poor point depressants; and

[0051] detergents.

[0052] An automatic transmission fluid should meet or exceed the specifications of the car manufacturer. An example of a suitable ATF is GM DEX-CVT®, which is a continuously variable transmission fluid meeting both GM 10028N and GM 9986219 specifications. Likewise, engine oils should generally meet the manufacturer's specification, and will usually meet the requirements of one of a number of commonly used service classifications, such as the American Petroleum Institute's classifications for gasoline and diesel engines. API classifications include SA, SB, SC, SD, SE, SF, SG, SH, and SJ for gasoline engines, and CA, CB, CC, CD, CE, CF, and CG for commercial oils sold for diesel engines. New classifications are being constantly developed to meet the requirements of modem engines as they are developed. Accordingly, the invention can also be practiced by adding an antifoam composition to any engine oils yet to be developed that meet or exceed any of the above classifications, or any future classification.

[0053] The base oils used in forming the functional fluids of the invention can be any suitable natural or synthetic oil having the necessary viscosity properties. Thus, the base oil may be composed entirely of a natural oil such as mineral oil of suitable viscosity or it may be composed entirely of a synthetic oil such as a poly-alpha-olefin of suitable viscosity. Likewise, the base oil may be a blend of natural and synthetic base oils provided that the blend has the requisite properties for use in the formation of an automatic transmission fluid. Ordinarily, the base oil should have a kinematic viscosity in the range of 2 to 50 centistokes, preferably 3 to 8 centistokes (cSt), at 100° C. Preferred base oils are Group III stocks. A preferred base oil viscosity is, for example, 3.8 cSt for the ratio of VHVI 2 and VHVI 4 that is used. In an embodiment of the present invention, the individual viscosities of those base stocks are 2.8 cSt and 4.3 cSt, respectively.

[0054] ATF's of the invention preferably contain detergent and dispersants. They function in part to solubilize fluid components and to suspend insoluble materials that build up over time during operation. In one embodiment, the detergent/dispersant contains a first component (such as an N-aliphatic alkyl substituted diethanolamine) and a second component comprising either an oil soluble phosphorus containing ashless dispersant and/or at least one oil-soluble boron-containing ashless dispersant. The ashless dispersants are present in amount such that the ratio of boron in the ashless dispersant is in the range of about 0.05 to about 0.2 part by weight of boron per part by weight of the first component, or the ratio of phosphorus in the ashless dispersant is about 0.1 to 0.4 parts per part by weight of the first component.

[0055] In one embodiment, the compositions of this invention contain at least one oil-soluble phosphorus- and boron-containing ashless dispersant present in an amount such that the ratio of phosphorus to the first component is in the range of about 0.15 to about 0.3 part by weight of phosphorus per part by weight of the first component, and such that the ratio of boron in the ashless dispersant is in the range of about 0.05 to about 0.15 part by weight of boron per part by weight of the first component.

[0056] Phosphorus- and/or boron-containing ashless dispersants can be formed by phosphorylating and/or boronating an ashless dispersant having basic nitrogen and/or at least one hydroxyl group in the molecule, such as a succinimide dispersant, succinic ester dispersant, succinic ester-amide dispersant, Mannich base dispersant, hydrocarbyl polyamine dispersant, or polymeric polyamine dispersant.

[0057] The ATF's also contain antiwear agents in a level suitable for protecting the moving components (e.g. the pump and the gears of the transmission) from wear. Typically, the antiwear additives will be present at a level of about 0.025 to about 5% by weight of the ATF. A non-limiting example of a suitable antiwear agent is 2,5-dimercapto-1,3,4-thiadiazole (DMTD) or derivatives thereof. To illustrate, derivatives of DMTD include:

[0058] a) 2-hydrocarbyldithio-5-mercapto-1,3,4-thiadiazole or 2,5-bis-(hydrocarbyldithio)-1,3,4-thiadiazole and mixtures thereof;

[0059] b) carboxylic esters of DMTD;

[0060] c) condensation products of halogenated aliphatic monocarboxylic acids with DMTD;

[0061] d) reaction products of unsaturated cyclic hydrocarbons and unsaturated ketones with DMTD;

[0062] e) reaction products of an aldehyde and diaryl amine with DMTD;

[0063] f) amine salts of DMTD;

[0064] g) dithiocarbamate derivatives of DMTD;

[0065] h) reaction products of an aldehyde and an alcohol or aromatic hydroxy compound and DMTD;

[0066] i) reaction products of an aldehyde, a mercaptan and DMTD;

[0067] j) 2-hydrocarbylthio-5-mercapto-1,3,4-thiadiazole; and

[0068] k) products from combining an oil soluble dispersant with DMTD; and mixtures thereof.

[0069] Compositions a)-k) are described, for example, in U.S. Pat. No. 4,612,129 and patent references cited therein, the disclosures of which are incorporated by reference. Thiadiazoles are commercially available, for example, from the Ethyl Corporation as HiTEC® 4313.

[0070] Depending on the base stocks that are chosen, an amount of seal swell agent may be required to meet the OEM seal compatibility requirements. Use of Group TI, Group III and Group IV base oils many times requires the addition of a material to swell seals. These materials may be chosen from the general categories of oil soluble diesters, aromatic base oils, and sulfones. Alkyl adipates are examples of soluble diesters that can be used. In a preferred embodiment, alkyl adipate is used at a treat rate of 3 to 20%, more preferably 3 to 10%, and most preferably about 5%.

[0071] A viscosity index improver is useful in the formulations and methods of the present invention and can include, but is not limited to, one or more materials selected from polyacrylate, polymethacrylate, styrene/olefin copolymer, styrene diene copolymer, EP copolymer or terpolymers, and combinations thereof. A preferred VI improver is a highly shear stable polymethacrylate polymer or copolymer used at, for example, about 15 percent by weight in the fluid formulation. VI improvers are commercially available.

[0072] The automatic transmission fluids of the invention may be used as lubricating compositions and hydraulic fluids in a variety of automotive transmissions. In one embodiment, the transmission has a sump volume of 13 liters (L) or less. In a preferred embodiment, the transmissions are continuously variable transmissions (CVT) with a sump of 9L or less, preferably 8L or less. One advantage of the ATF's of the invention is that they reduce foam or entrained air in an ATF. This has the effect of reducing or eliminating the pump whine caused by the implosion of air bubbles on the pressure side of the pump. Because of the high pressures involved, the problem is most pronounced in automatic transmissions in general, and in CVT's in particular. For this reason, in a preferred embodiment, the ATF's of the invention are used as hydraulic and lubricating fluids in continuously variable transmissions. The CVT's may be configured as transmissions for rear drive cars or as transaxles for front wheel drive cars.

[0073] One method of treating an engine or automatic transmission having a functional fluid therein according to the present invention includes the step of adding into the functional fluid a composition comprising an antifoam agent, with or without a diluent or carrier oil. This step of adding the antifoam agent composition may be performed by direct injection, such as by syringe, a metering apparatus, or otherwise. Also, this step may be performed at any of several stages during the lifetime of the vehicle—at the initial building of the transmission or engine; at its initial installation into a vehicle; at prescribed service intervals; when pump whine is or has been noticed; at any servicing, maintenance or rebuilding; at any topping off, filling or refilling of the with fluid; and at other times.

[0074] For example, one method according to the present invention comprises the steps of: (a) building a new automatic transrmission, (b) filling the transmission with ATF, (c) performing functional tests on the transmission, (d) removing some portion (e.g., one-half) of the ATF from the transmission, (e) adding an antifoam top treat composition into the partially-filled transmission, (f) shipping the transmission (e.g., to a dealer, service site, etc.), and (g) filling up the transmission with ATF. This process may optionally include the step of installing the transmission into a vehicle after step (a).

[0075] Alternatively, rather than adding the antifoam agent into the transmission (i.e., top treating the transmission), a method according to the present invention also includes the step of mixing the antifoam agent with an ATF prior to filling or topping off an automatic transmission with initial or additional ATF. The antifoam agent-rich ATF may then be used to fill, refill, or top off an automatic transmission, so as to reduce previously noticed pump whine or to guard against potential pump whine.

[0076] It should be noted that the step of adding the top treat composition or formulated ATF to a transmission according to the present invention may include adding such into the transmission case, the sump, the pump itself, a fill tube, a dipstick tube, a service port, the torque converter, the valve body, an accumulator, the hydraulic lines, or elsewhere in direct or indirect fluid communication with the pump. The location where the top treat or fully-formulated ATF is added may be proximate the transmission, or it may be at some relatively distant point from the transmission, such as at a suitable port in the pump/transmission hydraulic lines adjacent the radiator/condenser/oil cooler.

[0077] Likewise, antifoam compositions may be added to an engine at a number of suitable places, such as the engine block, oil pan, and the valley at the top of the engine block. Additions may be made at a number of engine inlets, such as the valve covers, oil inlet tubes, oil filler tubes, dipstick, and the like. Additional inlets may be provided in an engine if desired.

[0078] A method for reducing unwanted noise in an operating automatic transmission may be carried out by top treating the lubricating composition contained in the lubricant sump of the transmission with a top treat composition containing an antifoam compound such as described above. In a preferred embodiment, the antifoam compound is thermally stable, as measured by differential thermal analysis, to a temperature of 200° C. or more, preferably 400° C. or more, and most preferably 500° C. or more. As a general rule, the antifoam compound in the ATF's of the invention see the high temperatures at the imploding bubble surfaces for a relatively short period of time. For this reason, it is possible to use an antifoam agent with a thermal stability as measured by differential thermal analysis of less than the preferred ranges. However, for best results, it is preferred to use an antifoam agent that is thermodynamically stable at temperatures obtaining on the pressure side of the pump when the bubbles are adiabatically compressed.

[0079] The top treating of the lubricating composition in the sump may be carried out after assembly of the transmission at a transmission plant and before shipping the transmission to an automotive assembly line. Alternatively or in addition, the top treating step may be carried out at the automotive assembly line prior to shipping the car containing the transmission to a customer.

[0080] In the aftermarket, the top treating step may be carried out during scheduled maintenance of the transmission, or when the operator of a vehicle notices a noise originating from the transmission. The top treating step may be carried out by an automotive technician at a repair facility, or may be performed by the consumer.

[0081] The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. 

We claim:
 1. An functional fluid comprising: a) a lubricating oil; b) an antiwear agent; and c) an antifoam composition comprising a perfluoropolyether compound.
 2. A fluid according to claim 1, wherein the perfluoropolyether compound comprises a plurality of —(C_(a)F_(2a)O)— repeating units, wherein a is from 1 to
 10. 3. A fluid according to claim 1, wherein the perfluoropolyether comprises repeating units of —(CF₂—CF(CF₃)—O)—.
 4. A fluid according to claim 1, wherein the perfluoropolyether comprises repeating units of —(CF₂—CF₂—CF₂—O)—.
 5. A fluid according to claim 1, wherein the perfluoropolyether comprises repeating units of —(CF₂—CF₂—O)—.
 6. A fluid according to claim 1, wherein the perfluoropolyether comprises repeating units of —(C_(b)F_(2b)O)— and —(CF₂—O)—, wherein b is 2-10.
 7. A fluid according to claim 2, wherein the perfluoropolyether further comprises one or more functional groups selected from the group consisting of alkyl amide, silane, phosphate, carboxyl, ester, and hydroxyl.
 8. A fluid according to claim 1, wherein the fluid comprises 0.0005% to 1% by weight of the perfluoropolyether compound.
 9. A fluid according to claim 8, comprising an engine oil meeting or exceeding the minimum requirements of API service classification SF.
 10. A fluid according to claim 8, comprising an engine oil meeting or exceeding the minimum requirements of API service classification SJ.
 11. A fluid according to claim 8, comprising an engine oil meeting or exceeding the minimum requirements of API service classification CE, CF, or CG.
 12. An engine comprising a crankcase and engine block defining a lubricant sump, wherein the lubricant sump contains a lubricating oil composition comprising: a) a lubricating oil; b) an antiwear agent; and c) an antifoam composition comprising a perfluoropolyether compound.
 13. An engine according to claim 12, wherein the perfluoropolyether compound comprises a plurality of —(C_(a)F_(2a)O) repeating units, wherein a is from 1 to
 10. 14. An engine according to claim 12, wherein the perfluoropolyether comprises repeating units of (CF₂—CF(CF₃)—O)—.
 15. An engine according to claim 12, wherein the perfluoropolyether comprises repeating units of —(CF₂—CF₂—CF₂—O)—.
 16. An engine according to claim 12, wherein the perfluoropolyether comprises repeating units of —(C_(b)F_(2b)O)— and —(CF₂—O)—, wherein b is 2-10.
 17. An engine according to claim 13, wherein the perfluoropolyether further comprises one or more functional groups selected from the group consisting of alkyl amide, silane, phosphate, carboxyl, ester, and hydroxyl.
 18. An engine according to claim 12, wherein the fluid comprises 0.0005% to 1% by weight of the perfluoropolyether compound.
 19. An engine according to claim 12, wherein the engine is a gasoline engine.
 20. An engine according to claim 12, wherein the engine is a diesel engine.
 21. A method of treating an engine, the engine comprising a crankcase and engine block defining a lubricant sump, wherein the sump contains a lubricating composition, the method comprising adding to the lubricating composition in the sump a top treat composition comprising a perfluoropolyether compound.
 22. A method according to claim 21, wherein the perfluoropolyether compound comprises a plurality of —(C_(a)F_(2a)O)— repeating units, wherein a is from 1 to
 10. 23. A method according to claim 21, wherein the perfluoropolyether compound comprises repeating units of —(CF₂—CF(CF₃)—O)—.
 24. A method according to claim 21, wherein the perfluoropolyether compound comprises repeating units of —(CF₂—CF₂—CF₂—O)—.
 25. A method according to claim 21, wherein the perfluoropolyether compound comprises repeating units of —(CF₂—CF₂—O)—.
 26. A method according to claim 21, wherein the perfluoropolyether compound comprises repeating units of —(C_(b)F_(2b)O)— and —(CF₂—O)—, wherein b is 2-10.
 27. A method according to claim 21, wherein the perfluoropolyether compound comprises one or more functional groups selected from the group consisting of alkyl amide, silane, phosphate, carboxyl, ester, and hydroxyl.
 28. A method according to claim 21, wherein the fluid comprises 0.0005% to 1% by weight of the perfluoropolyether compound.
 29. A method according to claim 28, wherein the engine is a gasoline engine.
 30. A method according to claim 28, wherein the engine is a diesel engine.
 31. A method for reducing foam in an operating engine, the engine comprising a lubricant sump containing a lubricating composition, the method comprising top treating the lubricating composition in the lubricant sump with a top treat composition comprising an antifoam compound thermally stable, as measured by differential thermal analysis, to a temperature of higher than 500° C.
 32. A method according to claim 31, wherein the top treating is carried out after assembly of the engine and before shipping the engine to an automotive assembly line.
 33. A method according to claim 31, wherein the top treating is carried out at an automotive assembly line prior to shipping the car containing the engine to a customer.
 34. A method according to claim 31, wherein the top treating is carried out during scheduled maintenance of the engine.
 35. A method according to claim 31, wherein the antifoam composition comprises a perfluoropolyether.
 36. A method according to claim 35, wherein the perfluoropolyether compound comprises a plurality of —(C_(a)F_(2a)O)— repeating units, wherein a is from 1 to
 10. 37. A method according to claim 35, wherein the perfluoropolyether compound comprises repeating units of —(CF₂—CF(CF₃)—O)—.
 38. A method according to claim 35, wherein the perfluoropolyether compound comprises repeating units of —(C_(b)F_(2b)O)— and —(CF₂—O)—, wherein b is 2-10.
 39. A method according to claim 35, wherein the perfluoropolyether compound comprises one or more functional groups selected from the group consisting of alkyl amide, silane, phosphate, carboxyl, ester, and hydroxyl.
 40. A method according to claim 35, wherein the fluid comprises 0.0005% to 1% by weight of the perfluoropolyether compound after the top treating. 